2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcPat]{Typechecking patterns}
7 module TcPat ( tcPat, tcPats, tcOverloadedLit,
8 PatCtxt(..), badFieldCon, polyPatSig ) where
10 #include "HsVersions.h"
12 import {-# SOURCE #-} TcExpr( tcSyntaxOp )
13 import HsSyn ( Pat(..), LPat, HsConDetails(..), HsLit(..), HsOverLit(..), HsExpr(..),
14 LHsBinds, emptyLHsBinds, isEmptyLHsBinds,
15 collectPatsBinders, nlHsLit )
16 import TcHsSyn ( TcId, hsLitType )
18 import Inst ( InstOrigin(..), shortCutFracLit, shortCutIntLit,
19 newDicts, instToId, tcInstStupidTheta, isHsVar
21 import Id ( Id, idType, mkLocalId )
22 import CoreFVs ( idFreeTyVars )
23 import Name ( Name, mkSystemVarName )
24 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
25 import TcEnv ( newLocalName, tcExtendIdEnv1, tcExtendTyVarEnv2,
26 tcLookupClass, tcLookupDataCon, tcLookupId, refineEnvironment,
28 import TcMType ( newFlexiTyVarTy, arityErr, tcInstSkolTyVars, newBoxyTyVar, zonkTcType )
29 import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType,
31 BoxySigmaType, BoxyRhoType,
32 pprSkolTvBinding, isRefineableTy, isRigidTy, tcTyVarsOfTypes, mkTyVarTy, lookupTyVar,
33 emptyTvSubst, substTyVar, substTy, mkTopTvSubst, zipTopTvSubst, zipOpenTvSubst,
34 mkTyVarTys, mkClassPred, mkTyConApp, isOverloadedTy,
35 mkFunTy, mkFunTys, exactTyVarsOfTypes,
37 import VarSet ( elemVarSet, mkVarSet )
38 import Kind ( liftedTypeKind, openTypeKind )
39 import TcUnify ( boxySplitTyConApp, boxySplitListTy,
40 unBox, stripBoxyType, zapToMonotype,
41 boxyMatchTypes, boxyUnify, boxyUnifyList, checkSigTyVarsWrt )
42 import TcHsType ( UserTypeCtxt(..), tcPatSig )
43 import TysWiredIn ( boolTy, parrTyCon, tupleTyCon )
44 import Unify ( MaybeErr(..), gadtRefineTys )
45 import Type ( substTys, substTheta )
46 import StaticFlags ( opt_IrrefutableTuples )
47 import TyCon ( TyCon )
48 import DataCon ( DataCon, dataConTyCon, isVanillaDataCon,
49 dataConFieldLabels, dataConSourceArity, dataConSig )
50 import PrelNames ( integralClassName, fromIntegerName, integerTyConName,
51 fromRationalName, rationalTyConName )
52 import BasicTypes ( isBoxed )
53 import SrcLoc ( Located(..), SrcSpan, noLoc )
54 import ErrUtils ( Message )
55 import Util ( takeList, zipEqual )
61 %************************************************************************
65 %************************************************************************
69 -> [LPat Name] -- Patterns,
70 -> [BoxySigmaType] -- and their types
71 -> BoxyRhoType -- Result type,
72 -> (BoxyRhoType -> TcM a) -- and the checker for the body
73 -> TcM ([LPat TcId], a)
75 -- This is the externally-callable wrapper function
76 -- Typecheck the patterns, extend the environment to bind the variables,
77 -- do the thing inside, use any existentially-bound dictionaries to
78 -- discharge parts of the returning LIE, and deal with pattern type
81 -- 1. Initialise the PatState
82 -- 2. Check the patterns
83 -- 3. Apply the refinement
85 -- 5. Check that no existentials escape
87 tcPats ctxt pats tys res_ty thing_inside
88 = do { let init_state = PS { pat_ctxt = ctxt, pat_reft = emptyTvSubst }
90 ; (pats', ex_tvs, res) <- tc_lpats init_state pats tys $ \ pstate' ->
91 refineEnvironment (pat_reft pstate') $
92 thing_inside (refineType (pat_reft pstate') res_ty)
94 ; tcCheckExistentialPat ctxt pats' ex_tvs tys res_ty
96 ; returnM (pats', res) }
101 -> LPat Name -> BoxySigmaType
102 -> BoxyRhoType -- Result type
103 -> (BoxyRhoType -> TcM a) -- Checker for body, given its result type
104 -> TcM (LPat TcId, a)
105 tcPat ctxt pat pat_ty res_ty thing_inside
106 = do { ([pat'],thing) <- tcPats ctxt [pat] [pat_ty] res_ty thing_inside
107 ; return (pat', thing) }
111 tcCheckExistentialPat :: PatCtxt
112 -> [LPat TcId] -- Patterns (just for error message)
113 -> [TcTyVar] -- Existentially quantified tyvars bound by pattern
114 -> [BoxySigmaType] -- Types of the patterns
115 -> BoxyRhoType -- Type of the body of the match
116 -- Tyvars in either of these must not escape
118 -- NB: we *must* pass "pats_tys" not just "body_ty" to tcCheckExistentialPat
119 -- For example, we must reject this program:
120 -- data C = forall a. C (a -> Int)
122 -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int).
124 tcCheckExistentialPat ctxt pats [] pat_tys body_ty
125 = return () -- Short cut for case when there are no existentials
127 tcCheckExistentialPat (LetPat _) pats ex_tvs pat_tys body_ty
128 -- Don't know how to deal with pattern-bound existentials yet
129 = failWithTc (existentialExplode pats)
131 tcCheckExistentialPat ctxt pats ex_tvs pat_tys body_ty
132 = addErrCtxtM (sigPatCtxt (collectPatsBinders pats) ex_tvs pat_tys) $
133 checkSigTyVarsWrt (tcTyVarsOfTypes (body_ty:pat_tys)) ex_tvs
137 pat_reft :: GadtRefinement -- Binds rigid TcTyVars to their refinements
142 | LetPat (Name -> Maybe TcRhoType) -- Used for let(rec) bindings
144 patSigCtxt :: PatState -> UserTypeCtxt
145 patSigCtxt (PS { pat_ctxt = LetPat _ }) = BindPatSigCtxt
146 patSigCtxt other = LamPatSigCtxt
151 %************************************************************************
155 %************************************************************************
158 tcPatBndr :: PatState -> Name -> BoxySigmaType -> TcM TcId
159 tcPatBndr (PS { pat_ctxt = LamPat }) bndr_name pat_ty
160 = do { pat_ty' <- unBox pat_ty
161 -- We have an undecorated binder, so we do rule ABS1,
162 -- by unboxing the boxy type, forcing any un-filled-in
163 -- boxes to become monotypes
164 -- NB that pat_ty' can still be a polytype:
165 -- data T = MkT (forall a. a->a)
166 -- f t = case t of { MkT g -> ... }
167 -- Here, the 'g' must get type (forall a. a->a) from the
169 ; return (mkLocalId bndr_name pat_ty') }
171 tcPatBndr (PS { pat_ctxt = LetPat lookup_sig }) bndr_name pat_ty
172 | Just mono_ty <- lookup_sig bndr_name
173 = do { mono_name <- newLocalName bndr_name
174 ; boxyUnify mono_ty pat_ty
175 ; return (mkLocalId mono_name mono_ty) }
178 = do { pat_ty' <- unBox pat_ty
179 ; mono_name <- newLocalName bndr_name
180 ; return (mkLocalId mono_name pat_ty') }
184 bindInstsOfPatId :: TcId -> TcM a -> TcM (a, LHsBinds TcId)
185 bindInstsOfPatId id thing_inside
186 | not (isOverloadedTy (idType id))
187 = do { res <- thing_inside; return (res, emptyLHsBinds) }
189 = do { (res, lie) <- getLIE thing_inside
190 ; binds <- bindInstsOfLocalFuns lie [id]
191 ; return (res, binds) }
195 %************************************************************************
197 The main worker functions
199 %************************************************************************
203 tcPat takes a "thing inside" over which the patter scopes. This is partly
204 so that tcPat can extend the environment for the thing_inside, but also
205 so that constraints arising in the thing_inside can be discharged by the
208 This does not work so well for the ErrCtxt carried by the monad: we don't
209 want the error-context for the pattern to scope over the RHS.
210 Hence the getErrCtxt/setErrCtxt stuff in tc_lpats.
217 -> (PatState -> TcM a)
218 -> TcM ([LPat TcId], [TcTyVar], a)
220 tc_lpats pstate pats pat_tys thing_inside
221 = do { err_ctxt <- getErrCtxt
222 ; let loop pstate [] []
223 = do { res <- thing_inside pstate
224 ; return ([], [], res) }
226 loop pstate (p:ps) (ty:tys)
227 = do { (p', p_tvs, (ps', ps_tvs, res))
228 <- tc_lpat pstate p ty $ \ pstate' ->
229 setErrCtxt err_ctxt $
231 -- setErrCtxt: restore context before doing the next pattern
232 -- See note [Nesting] above
234 ; return (p':ps', p_tvs ++ ps_tvs, res) }
236 loop _ _ _ = pprPanic "tc_lpats" (ppr pats $$ ppr pat_tys)
238 ; loop pstate pats pat_tys }
244 -> (PatState -> TcM a)
245 -> TcM (LPat TcId, [TcTyVar], a)
246 tc_lpat pstate (L span pat) pat_ty thing_inside
248 maybeAddErrCtxt (patCtxt pat) $
249 do { let pat_ty' = refineType (pat_reft pstate) pat_ty
250 -- Make sure the result type reflects the current refinement
251 ; (pat', tvs, res) <- tc_pat pstate pat pat_ty' thing_inside
252 ; return (L span pat', tvs, res) }
257 -> Pat Name -> BoxySigmaType -- Fully refined result type
258 -> (PatState -> TcM a) -- Thing inside
259 -> TcM (Pat TcId, -- Translated pattern
260 [TcTyVar], -- Existential binders
261 a) -- Result of thing inside
263 tc_pat pstate (VarPat name) pat_ty thing_inside
264 = do { id <- tcPatBndr pstate name pat_ty
265 ; (res, binds) <- bindInstsOfPatId id $
266 tcExtendIdEnv1 name id $
267 (traceTc (text "binding" <+> ppr name <+> ppr (idType id))
268 >> thing_inside pstate)
269 ; let pat' | isEmptyLHsBinds binds = VarPat id
270 | otherwise = VarPatOut id binds
271 ; return (pat', [], res) }
273 tc_pat pstate (ParPat pat) pat_ty thing_inside
274 = do { (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
275 ; return (ParPat pat', tvs, res) }
277 tc_pat pstate (BangPat pat) pat_ty thing_inside
278 = do { (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
279 ; return (BangPat pat', tvs, res) }
281 -- There's a wrinkle with irrefutable patterns, namely that we
282 -- must not propagate type refinement from them. For example
283 -- data T a where { T1 :: Int -> T Int; ... }
284 -- f :: T a -> Int -> a
286 -- It's obviously not sound to refine a to Int in the right
287 -- hand side, because the arugment might not match T1 at all!
289 -- Nor should a lazy pattern bind any existential type variables
290 -- because they won't be in scope when we do the desugaring
291 tc_pat pstate lpat@(LazyPat pat) pat_ty thing_inside
292 = do { (pat', pat_tvs, res) <- tc_lpat pstate pat pat_ty $ \ _ ->
294 -- Ignore refined pstate',
296 -- Check no existentials
297 ; if (null pat_tvs) then return ()
298 else lazyPatErr lpat pat_tvs
300 -- Check that the pattern has a lifted type
301 ; pat_tv <- newBoxyTyVar liftedTypeKind
302 ; boxyUnify pat_ty (mkTyVarTy pat_tv)
304 ; return (LazyPat pat', [], res) }
306 tc_pat pstate (WildPat _) pat_ty thing_inside
307 = do { pat_ty' <- unBox pat_ty -- Make sure it's filled in with monotypes
308 ; res <- thing_inside pstate
309 ; return (WildPat pat_ty', [], res) }
311 tc_pat pstate (AsPat (L nm_loc name) pat) pat_ty thing_inside
312 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
313 ; (pat', tvs, res) <- tcExtendIdEnv1 name bndr_id $
314 tc_lpat pstate pat (idType bndr_id) thing_inside
315 -- NB: if we do inference on:
316 -- \ (y@(x::forall a. a->a)) = e
317 -- we'll fail. The as-pattern infers a monotype for 'y', which then
318 -- fails to unify with the polymorphic type for 'x'. This could
319 -- perhaps be fixed, but only with a bit more work.
321 -- If you fix it, don't forget the bindInstsOfPatIds!
322 ; return (AsPat (L nm_loc bndr_id) pat', tvs, res) }
324 -- Type signatures in patterns
325 -- See Note [Pattern coercions] below
326 tc_pat pstate (SigPatIn pat sig_ty) pat_ty thing_inside
327 = do { (inner_ty, tv_binds) <- tcPatSig (patSigCtxt pstate) sig_ty pat_ty
328 ; (pat', tvs, res) <- tcExtendTyVarEnv2 tv_binds $
329 tc_lpat pstate pat inner_ty thing_inside
330 ; return (SigPatOut pat' inner_ty, tvs, res) }
332 tc_pat pstate pat@(TypePat ty) pat_ty thing_inside
333 = failWithTc (badTypePat pat)
335 ------------------------
336 -- Lists, tuples, arrays
337 tc_pat pstate (ListPat pats _) pat_ty thing_inside
338 = do { elt_ty <- boxySplitListTy pat_ty
339 ; let elt_tys = takeList pats (repeat elt_ty)
340 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
341 ; return (ListPat pats' elt_ty, pats_tvs, res) }
343 tc_pat pstate (PArrPat pats _) pat_ty thing_inside
344 = do { [elt_ty] <- boxySplitTyConApp parrTyCon pat_ty
345 ; let elt_tys = takeList pats (repeat elt_ty)
346 ; (pats', pats_tvs, res) <- tc_lpats pstate pats elt_tys thing_inside
347 ; ifM (null pats) (zapToMonotype pat_ty) -- c.f. ExplicitPArr in TcExpr
348 ; return (PArrPat pats' elt_ty, pats_tvs, res) }
350 tc_pat pstate (TuplePat pats boxity _) pat_ty thing_inside
351 = do { arg_tys <- boxySplitTyConApp (tupleTyCon boxity (length pats)) pat_ty
352 ; (pats', pats_tvs, res) <- tc_lpats pstate pats arg_tys thing_inside
354 -- Under flag control turn a pattern (x,y,z) into ~(x,y,z)
355 -- so that we can experiment with lazy tuple-matching.
356 -- This is a pretty odd place to make the switch, but
357 -- it was easy to do.
358 ; let unmangled_result = TuplePat pats' boxity pat_ty
359 possibly_mangled_result
360 | opt_IrrefutableTuples && isBoxed boxity = LazyPat (noLoc unmangled_result)
361 | otherwise = unmangled_result
363 ; ASSERT( length arg_tys == length pats ) -- Syntactically enforced
364 return (possibly_mangled_result, pats_tvs, res) }
366 ------------------------
368 tc_pat pstate pat_in@(ConPatIn (L con_span con_name) arg_pats) pat_ty thing_inside
369 = do { data_con <- tcLookupDataCon con_name
370 ; let tycon = dataConTyCon data_con
371 ; tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside }
373 ------------------------
375 tc_pat pstate (LitPat simple_lit) pat_ty thing_inside
376 = do { boxyUnify (hsLitType simple_lit) pat_ty
377 ; res <- thing_inside pstate
378 ; returnM (LitPat simple_lit, [], res) }
380 ------------------------
381 -- Overloaded patterns: n, and n+k
382 tc_pat pstate pat@(NPat over_lit mb_neg eq _) pat_ty thing_inside
383 = do { let orig = LiteralOrigin over_lit
384 ; lit' <- tcOverloadedLit orig over_lit pat_ty
385 ; eq' <- tcSyntaxOp orig eq (mkFunTys [pat_ty, pat_ty] boolTy)
386 ; mb_neg' <- case mb_neg of
387 Nothing -> return Nothing -- Positive literal
388 Just neg -> -- Negative literal
389 -- The 'negate' is re-mappable syntax
390 do { neg' <- tcSyntaxOp orig neg (mkFunTy pat_ty pat_ty)
391 ; return (Just neg') }
392 ; res <- thing_inside pstate
393 ; returnM (NPat lit' mb_neg' eq' pat_ty, [], res) }
395 tc_pat pstate pat@(NPlusKPat (L nm_loc name) lit ge minus) pat_ty thing_inside
396 = do { bndr_id <- setSrcSpan nm_loc (tcPatBndr pstate name pat_ty)
397 ; let pat_ty' = idType bndr_id
398 orig = LiteralOrigin lit
399 ; lit' <- tcOverloadedLit orig lit pat_ty'
401 -- The '>=' and '-' parts are re-mappable syntax
402 ; ge' <- tcSyntaxOp orig ge (mkFunTys [pat_ty', pat_ty'] boolTy)
403 ; minus' <- tcSyntaxOp orig minus (mkFunTys [pat_ty', pat_ty'] pat_ty')
405 -- The Report says that n+k patterns must be in Integral
406 -- We may not want this when using re-mappable syntax, though (ToDo?)
407 ; icls <- tcLookupClass integralClassName
408 ; dicts <- newDicts orig [mkClassPred icls [pat_ty']]
411 ; res <- tcExtendIdEnv1 name bndr_id (thing_inside pstate)
412 ; returnM (NPlusKPat (L nm_loc bndr_id) lit' ge' minus', [], res) }
416 %************************************************************************
418 Most of the work for constructors is here
419 (the rest is in the ConPatIn case of tc_pat)
421 %************************************************************************
424 tcConPat :: PatState -> SrcSpan -> DataCon -> TyCon
425 -> BoxySigmaType -- Type of the pattern
426 -> HsConDetails Name (LPat Name) -> (PatState -> TcM a)
427 -> TcM (Pat TcId, [TcTyVar], a)
428 tcConPat pstate con_span data_con tycon pat_ty arg_pats thing_inside
429 | isVanillaDataCon data_con
430 = do { ty_args <- boxySplitTyConApp tycon pat_ty
431 ; let (tvs, _, arg_tys, _, _) = dataConSig data_con
432 arg_tvs = exactTyVarsOfTypes arg_tys
433 -- See Note [Silly type synonyms in smart-app] in TcExpr
434 -- for why we must use exactTyVarsOfTypes
435 inst_prs = zipEqual "tcConPat" tvs ty_args
436 subst = mkTopTvSubst inst_prs
437 arg_tys' = substTys subst arg_tys
438 unconstrained_ty_args = [ty_arg | (tv,ty_arg) <- inst_prs,
439 not (tv `elemVarSet` arg_tvs)]
440 ; mapM unBox unconstrained_ty_args -- Zap these to monotypes
441 ; tcInstStupidTheta data_con ty_args
442 ; traceTc (text "tcConPat" <+> vcat [ppr data_con, ppr ty_args, ppr arg_tys'])
443 ; (arg_pats', tvs, res) <- tcConArgs pstate data_con arg_pats arg_tys' thing_inside
444 ; return (ConPatOut (L con_span data_con) [] [] emptyLHsBinds
445 arg_pats' (mkTyConApp tycon ty_args),
448 | otherwise -- GADT case
449 = do { ty_args <- boxySplitTyConApp tycon pat_ty
450 ; span <- getSrcSpanM -- The whole pattern
452 -- Instantiate the constructor type variables and result type
453 ; let (tvs, theta, arg_tys, _, res_tys) = dataConSig data_con
454 arg_tvs = exactTyVarsOfTypes arg_tys
455 -- See Note [Silly type synonyms in smart-app] in TcExpr
456 -- for why we must use exactTyVarsOfTypes
457 skol_info = PatSkol data_con span
458 arg_flags = [ tv `elemVarSet` arg_tvs | tv <- tvs ]
459 ; tvs' <- tcInstSkolTyVars skol_info tvs
460 ; let res_tys' = substTys (zipTopTvSubst tvs (mkTyVarTys tvs')) res_tys
462 -- Do type refinement!
463 ; traceTc (text "tcGadtPat" <+> vcat [ppr data_con, ppr tvs', ppr res_tys',
464 text "ty-args:" <+> ppr ty_args ])
465 ; refineAlt pstate data_con tvs' arg_flags res_tys' ty_args
466 $ \ pstate' tv_tys' -> do
468 -- ToDo: arg_tys should be boxy, but I don't think theta' should be,
469 -- or the tv_tys' in the call to tcInstStupidTheta
470 { let tenv' = zipTopTvSubst tvs tv_tys'
471 theta' = substTheta tenv' theta
472 arg_tys' = substTys tenv' arg_tys -- Boxy types
474 ; ((arg_pats', inner_tvs, res), lie_req) <- getLIE $
475 do { tcInstStupidTheta data_con tv_tys'
476 -- The stupid-theta mentions the newly-bound tyvars, so
477 -- it must live inside the getLIE, so that the
478 -- tcSimplifyCheck will apply the type refinement to it
479 ; tcConArgs pstate' data_con arg_pats arg_tys' thing_inside }
481 ; dicts <- newDicts (SigOrigin skol_info) theta'
482 ; dict_binds <- tcSimplifyCheck doc tvs' dicts lie_req
484 ; return (ConPatOut (L con_span data_con)
485 tvs' (map instToId dicts) dict_binds
486 arg_pats' (mkTyConApp tycon ty_args),
487 tvs' ++ inner_tvs, res)
490 doc = ptext SLIT("existential context for") <+> quotes (ppr data_con)
492 tcConArgs :: PatState -> DataCon
493 -> HsConDetails Name (LPat Name) -> [TcSigmaType]
494 -> (PatState -> TcM a)
495 -> TcM (HsConDetails TcId (LPat Id), [TcTyVar], a)
497 tcConArgs pstate data_con (PrefixCon arg_pats) arg_tys thing_inside
498 = do { checkTc (con_arity == no_of_args) -- Check correct arity
499 (arityErr "Constructor" data_con con_arity no_of_args)
500 ; (arg_pats', tvs, res) <- tc_lpats pstate arg_pats arg_tys thing_inside
501 ; return (PrefixCon arg_pats', tvs, res) }
503 con_arity = dataConSourceArity data_con
504 no_of_args = length arg_pats
506 tcConArgs pstate data_con (InfixCon p1 p2) arg_tys thing_inside
507 = do { checkTc (con_arity == 2) -- Check correct arity
508 (arityErr "Constructor" data_con con_arity 2)
509 ; ([p1',p2'], tvs, res) <- tc_lpats pstate [p1,p2] arg_tys thing_inside
510 ; return (InfixCon p1' p2', tvs, res) }
512 con_arity = dataConSourceArity data_con
514 tcConArgs pstate data_con (RecCon rpats) arg_tys thing_inside
515 = do { (rpats', tvs, res) <- tc_fields pstate rpats thing_inside
516 ; return (RecCon rpats', tvs, res) }
518 tc_fields :: PatState -> [(Located Name, LPat Name)]
519 -> (PatState -> TcM a)
520 -> TcM ([(Located TcId, LPat TcId)], [TcTyVar], a)
521 tc_fields pstate [] thing_inside
522 = do { res <- thing_inside pstate
523 ; return ([], [], res) }
525 tc_fields pstate (rpat : rpats) thing_inside
526 = do { (rpat', tvs1, (rpats', tvs2, res))
527 <- tc_field pstate rpat $ \ pstate' ->
528 tc_fields pstate' rpats thing_inside
529 ; return (rpat':rpats', tvs1 ++ tvs2, res) }
531 tc_field pstate (field_lbl, pat) thing_inside
532 = do { (sel_id, pat_ty) <- wrapLocFstM find_field_ty field_lbl
533 ; (pat', tvs, res) <- tc_lpat pstate pat pat_ty thing_inside
534 ; return ((sel_id, pat'), tvs, res) }
536 find_field_ty field_lbl
537 = case [ty | (f,ty) <- field_tys, f == field_lbl] of
539 -- No matching field; chances are this field label comes from some
540 -- other record type (or maybe none). As well as reporting an
541 -- error we still want to typecheck the pattern, principally to
542 -- make sure that all the variables it binds are put into the
543 -- environment, else the type checker crashes later:
544 -- f (R { foo = (a,b) }) = a+b
545 -- If foo isn't one of R's fields, we don't want to crash when
546 -- typechecking the "a+b".
547 [] -> do { addErrTc (badFieldCon data_con field_lbl)
548 ; bogus_ty <- newFlexiTyVarTy liftedTypeKind
549 ; return (error "Bogus selector Id", bogus_ty) }
551 -- The normal case, when the field comes from the right constructor
553 ASSERT( null extras )
554 do { sel_id <- tcLookupId field_lbl
555 ; return (sel_id, pat_ty) }
557 field_tys = zip (dataConFieldLabels data_con) arg_tys
558 -- Don't use zipEqual! If the constructor isn't really a record, then
559 -- dataConFieldLabels will be empty (and each field in the pattern
560 -- will generate an error below).
564 %************************************************************************
568 %************************************************************************
571 refineAlt :: PatState
572 -> DataCon -- For tracing only
573 -> [TcTyVar] -- Type variables from pattern
574 -> [Bool] -- Flags indicating which type variables occur
575 -- in the type of at least one argument
576 -> [TcType] -- Result types from the pattern
577 -> [BoxySigmaType] -- Result types from the scrutinee (context)
578 -> (PatState -> [BoxySigmaType] -> TcM a)
579 -- Possibly-refined existentials
581 refineAlt pstate con pat_tvs arg_flags pat_res_tys ctxt_res_tys thing_inside
582 | not (all isRigidTy ctxt_res_tys)
583 -- The context is not a rigid type, so we do no type refinement here.
584 = do { let arg_tvs = mkVarSet [ tv | (tv, True) <- pat_tvs `zip` arg_flags]
585 subst = boxyMatchTypes arg_tvs pat_res_tys ctxt_res_tys
587 res_tvs = tcTyVarsOfTypes pat_res_tys
588 -- The tvs are (already) all fresh skolems. We need a
589 -- fresh skolem for each type variable (to bind in the pattern)
590 -- even if it's refined away by the type refinement
592 | not (tv `elemVarSet` res_tvs) = return (mkTyVarTy tv)
593 | Just boxy_ty <- lookupTyVar subst tv = return boxy_ty
594 | otherwise = do { tv <- newBoxyTyVar openTypeKind
595 ; return (mkTyVarTy tv) }
596 ; pat_tys' <- mapM find_inst pat_tvs
598 -- Do the thing inside
599 ; res <- thing_inside pstate pat_tys'
601 -- Unbox the types that have been filled in by the thing_inside
602 -- I.e. the ones whose type variables are mentioned in at least one arg
603 ; let strip ty in_arg_tv | in_arg_tv = stripBoxyType ty
604 | otherwise = return ty
605 ; pat_tys'' <- zipWithM strip pat_tys' arg_flags
606 ; let subst = zipOpenTvSubst pat_tvs pat_tys''
607 ; boxyUnifyList (substTys subst pat_res_tys) ctxt_res_tys
609 ; return res } -- All boxes now filled
611 | otherwise -- The context is rigid, so we can do type refinement
612 = case gadtRefineTys (pat_reft pstate) con pat_tvs pat_res_tys ctxt_res_tys of
613 Failed msg -> failWithTc (inaccessibleAlt msg)
614 Succeeded (new_subst, all_bound_here)
615 | all_bound_here -- All the new bindings are for pat_tvs, so no need
616 -- to refine the environment or pstate
617 -> do { traceTc trace_msg
618 ; thing_inside pstate pat_tvs' }
619 | otherwise -- New bindings affect the context, so pass down pstate'.
620 -- DO NOT refine the envt, because we might be inside a
622 -> do { traceTc trace_msg
623 ; thing_inside pstate' pat_tvs' }
625 pat_tvs' = map (substTyVar new_subst) pat_tvs
626 pstate' = pstate { pat_reft = new_subst }
627 trace_msg = text "refineTypes:match" <+> ppr con <+> ppr new_subst
629 refineType :: GadtRefinement -> BoxyRhoType -> BoxyRhoType
630 -- Refine the type if it is rigid
632 | isRefineableTy ty = substTy reft ty
637 %************************************************************************
641 %************************************************************************
643 In tcOverloadedLit we convert directly to an Int or Integer if we
644 know that's what we want. This may save some time, by not
645 temporarily generating overloaded literals, but it won't catch all
646 cases (the rest are caught in lookupInst).
649 tcOverloadedLit :: InstOrigin
652 -> TcM (HsOverLit TcId)
653 tcOverloadedLit orig lit@(HsIntegral i fi) res_ty
654 | not (fi `isHsVar` fromIntegerName) -- Do not generate a LitInst for rebindable syntax.
655 -- Reason: If we do, tcSimplify will call lookupInst, which
656 -- will call tcSyntaxName, which does unification,
657 -- which tcSimplify doesn't like
658 -- ToDo: noLoc sadness
659 = do { integer_ty <- tcMetaTy integerTyConName
660 ; fi' <- tcSyntaxOp orig fi (mkFunTy integer_ty res_ty)
661 ; return (HsIntegral i (HsApp (noLoc fi') (nlHsLit (HsInteger i integer_ty)))) }
663 | Just expr <- shortCutIntLit i res_ty
664 = return (HsIntegral i expr)
667 = do { expr <- newLitInst orig lit res_ty
668 ; return (HsIntegral i expr) }
670 tcOverloadedLit orig lit@(HsFractional r fr) res_ty
671 | not (fr `isHsVar` fromRationalName) -- c.f. HsIntegral case
672 = do { rat_ty <- tcMetaTy rationalTyConName
673 ; fr' <- tcSyntaxOp orig fr (mkFunTy rat_ty res_ty)
674 -- Overloaded literals must have liftedTypeKind, because
675 -- we're instantiating an overloaded function here,
676 -- whereas res_ty might be openTypeKind. This was a bug in 6.2.2
677 -- However this'll be picked up by tcSyntaxOp if necessary
678 ; return (HsFractional r (HsApp (noLoc fr') (nlHsLit (HsRat r rat_ty)))) }
680 | Just expr <- shortCutFracLit r res_ty
681 = return (HsFractional r expr)
684 = do { expr <- newLitInst orig lit res_ty
685 ; return (HsFractional r expr) }
687 newLitInst :: InstOrigin -> HsOverLit Name -> BoxyRhoType -> TcM (HsExpr TcId)
688 newLitInst orig lit res_ty -- Make a LitInst
689 = do { loc <- getInstLoc orig
690 ; res_tau <- zapToMonotype res_ty
691 ; new_uniq <- newUnique
692 ; let lit_nm = mkSystemVarName new_uniq FSLIT("lit")
693 lit_inst = LitInst lit_nm lit res_tau loc
695 ; return (HsVar (instToId lit_inst)) }
699 %************************************************************************
701 Note [Pattern coercions]
703 %************************************************************************
705 In principle, these program would be reasonable:
707 f :: (forall a. a->a) -> Int
708 f (x :: Int->Int) = x 3
710 g :: (forall a. [a]) -> Bool
713 In both cases, the function type signature restricts what arguments can be passed
714 in a call (to polymorphic ones). The pattern type signature then instantiates this
715 type. For example, in the first case, (forall a. a->a) <= Int -> Int, and we
716 generate the translated term
717 f = \x' :: (forall a. a->a). let x = x' Int in x 3
719 From a type-system point of view, this is perfectly fine, but it's *very* seldom useful.
720 And it requires a significant amount of code to implement, becuase we need to decorate
721 the translated pattern with coercion functions (generated from the subsumption check
724 So for now I'm just insisting on type *equality* in patterns. No subsumption.
726 Old notes about desugaring, at a time when pattern coercions were handled:
728 A SigPat is a type coercion and must be handled one at at time. We can't
729 combine them unless the type of the pattern inside is identical, and we don't
730 bother to check for that. For example:
732 data T = T1 Int | T2 Bool
733 f :: (forall a. a -> a) -> T -> t
734 f (g::Int->Int) (T1 i) = T1 (g i)
735 f (g::Bool->Bool) (T2 b) = T2 (g b)
737 We desugar this as follows:
739 f = \ g::(forall a. a->a) t::T ->
741 in case t of { T1 i -> T1 (gi i)
744 in case t of { T2 b -> T2 (gb b)
747 Note that we do not treat the first column of patterns as a
748 column of variables, because the coerced variables (gi, gb)
749 would be of different types. So we get rather grotty code.
750 But I don't think this is a common case, and if it was we could
751 doubtless improve it.
753 Meanwhile, the strategy is:
754 * treat each SigPat coercion (always non-identity coercions)
756 * deal with the stuff inside, and then wrap a binding round
757 the result to bind the new variable (gi, gb, etc)
760 %************************************************************************
762 \subsection{Errors and contexts}
764 %************************************************************************
767 patCtxt :: Pat Name -> Maybe Message -- Not all patterns are worth pushing a context
768 patCtxt (VarPat _) = Nothing
769 patCtxt (ParPat _) = Nothing
770 patCtxt (AsPat _ _) = Nothing
771 patCtxt pat = Just (hang (ptext SLIT("In the pattern:"))
774 -----------------------------------------------
776 existentialExplode pats
777 = hang (vcat [text "My brain just exploded.",
778 text "I can't handle pattern bindings for existentially-quantified constructors.",
779 text "In the binding group for"])
780 4 (vcat (map ppr pats))
782 sigPatCtxt bound_ids bound_tvs tys tidy_env
783 = -- tys is (body_ty : pat_tys)
784 mapM zonkTcType tys `thenM` \ tys' ->
786 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
787 (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys'
790 sep [ptext SLIT("When checking an existential match that binds"),
791 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)),
792 ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys),
793 ptext SLIT("The body has type:") <+> ppr tidy_body_ty
796 show_ids = filter is_interesting bound_ids
797 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
799 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
800 -- Don't zonk the types so we get the separate, un-unified versions
802 badFieldCon :: DataCon -> Name -> SDoc
803 badFieldCon con field
804 = hsep [ptext SLIT("Constructor") <+> quotes (ppr con),
805 ptext SLIT("does not have field"), quotes (ppr field)]
807 polyPatSig :: TcType -> SDoc
809 = hang (ptext SLIT("Illegal polymorphic type signature in pattern:"))
812 badTypePat pat = ptext SLIT("Illegal type pattern") <+> ppr pat
816 hang (ptext SLIT("A lazy (~) pattern connot bind existential type variables"))
817 2 (vcat (map pprSkolTvBinding tvs))
820 = hang (ptext SLIT("Inaccessible case alternative:")) 2 msg